Surgical removal of epileptogenic brain is indicated for treatment of many medically refractory focal seizure disorders. One important factor in providing good results from such surgery is the degree of accuracy in identifying epileptogenic foci. Various methods and devices have been used in attempting to determine epileptogenic foci. All, of course, involve sensing of intracranial electrical activity using electrical contacts applied in various ways.
Standard scalp contacts have been used for many years, but accurate localization is usually very difficult with recordings obtained from such contacts. In recent years, therefore, many epilepsy centers have adopted techniques using intracranial contacts to better define regions of cortical epileptogenicity.
Intracranial sensing techniques have used, broadly speaking, two different kinds of members for engagement with brain tissue. Such tissue-engagement members include depth probes and flexible flat surface members.
Depth probes, which are often referred to as "depth electrodes," penetrate deep into the brain tissue in direct contact with such tissue. On the other hand, flat flexible surface members, including what are sometimes referred to as "strip" electrodes and "grid" electrodes, are placed subdurally in direct contact with brain tissue at the surface of the brain.
Each of these different kinds of intracranial tissue-engagement members has a plurality of electrodes which are separated from one another by a non-conductive material on which the electrodes are mounted. Separate lead wires extend from the tissue-engagement member for each electrode. Such lead wires extend away from the tissue-engagement member to means for connecting the lead wires with individual conductors, which lead to monitoring or recording equipment.
Depth probes typically have electrode rings sleeved over and spaced along a non-conductive tubular member, with thin insulated wires extending inside the tube to a position away from its tissue-engaging portion. An example of such depth probes is shown in U.S. Pat. No. 4,425,645 (Arseneault et al.).
Strips and grids have a one-dimensional line and a two-dimensional field, respectively, of electrode disks which are arranged and held on a non-conductive flat flexible sheet-like member, usually between two thin sheet-like layers of non-conductive material. Thin insulated wires typically extend between the layers to a proximal edge of the sheet-like member and from there as lead wires away from such tissue-engaging member. An example of such a strip electrode is disclosed in U.S. patent application No. 71,075, now U.S. Pat. No. 4,805,625 (Wyler et al.).
For each type of tissue-engagement member used in the prior art for monitoring electrical activity in the brain, the procedures for placement and hookup are of great importance.
In the case of depth probes, it is essential that the depth probes be inserted with a high degree of accuracy in order to avoid damage to veins and arteries or unnecessary damage to brain tissue which might be caused by insertion and reinsertion. Precision in insertion is also necessary in order that placement be in the most advantageous positions for locating abnormal cells.
In the case of strip and grid electrodes, it is important that the flat flexible member be in proper contact with brain tissue to obtain reliable readings. It is also important that the often rather large opening in the skull, which is necessary for proper placement or insertion of a grid or strip, be well protected from the possibility of infection o that intracranial infection does not occur.
For both depth electrodes and strip or grid electrodes, it is essential that the lead wires extending from the brain-engagement member be properly connected and that the fragile lead wires themselves remain functional, without any breakage or disconnection.
While there has been much progress in the field of electrical brain-contact devices in recent years, existing devices and procedures have a number of problems and drawbacks. For one thing, the surgical placement and set-up procedures which precede the test period are far too time-consuming and complex. Such procedures in some cases also lead to specific problems.
Such problems can be described best by generally describing at least certain parts of the placement and set-up procedures.
One of the early steps in existing placement and set-up procedures for grid and strip electrodes is making an incision in the scalp over the site of proposed electrode placement. Then a burr hole is drilled in the skull or a skull area otherwise removed. One or more incisions are then made in the dura to accommodate placement of a grid or insertion of a strip. Dural tack-up sutures are placed in both dural margins.
The grid or strip electrode is then placed or inserted, with the electrodes in contact with the brain tissue. When strip electrodes are used, a plurality of strips are inserted in each burr hole. After the grid or strips have been positioned, the dural edges are approximated with a suture.
The lead wires, which extend from the proximal end of each strip or grid, are passed through the sutured dura incision. All the wires, one for each electrode on the grid or on every strip, are then brought out through the skin by passing them through a needle and then drawing them through the scalp at a distance (usually 4-5 cm) from the skull opening. When there are numerous wires it is often necessary to tunnel in a number of directions through the scalp to sites spaced from the skull opening. This can be both very time-consuming and very hard on the patient's head. Furthermore, when such wires have exited the scalp at the chosen sites, it then remains necessary to make electrical hookups of each of such wires in the appropriate manner. This is itself a time-consuming operation, and one in which there is a risk of incorrect hookups.
The fragile lead wires are quite susceptible to breakage during these manipulative operations. When this occurs, it may be necessary to reopen the dura to remove and replace the grid or strip from which the lead wire broke, and repeat many of the procedures described above.
In order to minimize the likelihood of lead wire breakage, lead wires of greater size may be used. However, increasing the diameter of the lead wires tends to increase the overall thickness of the strip or grid. Thickness can be undesirable in such flat flexible members and can in some cases pose problems for the electrical sensing operations. Furthermore, increasing wire thickness can substantially increase the cost of the device, particularly if silver or platinum wire is used.
Because of all the problems and difficulties of such wire exit and connection operations, lead wires are sometimes simply brought out of the head right at the point of the skull opening. This procedure results in a greater risk of fluid leakage problems and of dangerous infection occurring at the site of the major wound, near, of course, to the brain by virtue of such opening.
Referring now to the insertion and connection of depth probes, such electrodes have been installed in different ways depending upon the circumstances. In some cases, depth probes are stiffened by means of a stylette which is inserted into the tubular depth probe. The probe is then pushed into the brain tissue, guided by the stylette, and the stylette is then withdrawn. In other cases, such as when a cannula is already in place in the brain tissue, the cannula must be removed in order to accommodate insertion of the depth probe at that site, either with or without the aid of a stylette.
In either case, various securing steps are then carried out. After that, electrical connections are made, either with or without the aid of specialized connector means. Such connection procedures are typically difficult and time-consuming.
There remains a substantial need for an improved electrical brain-contact device overcoming the above problems and difficulties arising during placement and setup procedures.